Preeclampsia is a disease that affects up 10% of pregnancies globally and is the leading cause of maternal mortality and morbidity. There is not currently no effective therapy for this condition of vasospasm, endothelial damage and systemic inflammation. Data from mouse models of the targeted knock outs of complement components and regulators, a mouse model of antiphospholipid syndrome, and observational studies of human placentas supports involvement of complement activation in dysfunction of the placenta. In a histopathologically similar disease, aHUS, 50-60% of cases are associated with rare (heterozygous in <1% of the population) dysfunctional mutations. The functional deficits of the mutants have been characterized and the overwhelming majority, greater than 95%, have had a deficit that fits a model of increased or poorly regulated complement activation leading pathologic microthrombi. These findings led to the sequencing of membrane cofactor protein (MCP), complement factor I (FI), and complement factor H (FH) in a group of preeclamptic patients from the PROMISSE study (Predictors of pregnancy Outcome: biomarkers In antiphospholipid Syndrome and Systemic lupus Erythematosus). Rare variants were discovered in 7 of the 40 cases and in none of the 33 controls. Most of these had their functional deficit characterized and fit the existing model in aHUS of excessive complement activation causing the disease phenotype. Work done in this grant will use a two pronged approach of: targeted resequencing of cases and controls and experiments using primary placental samples, primary human trophoblast cells and trophoblast cell lines to further identify the role of the complement system in preeclampsia. Targeted resequencing of the initial population of PROMISSE patients will identify mutations in genes at loci implicated by linkage studies of families with preeclampsia and in the following pathways implicated by the literature: complement, thrombosis, cell cycle, apoptosis, angiogenesis, and endothelial cell activation. We will look at genes outside of the complement pathway as well as those in the pathway because the insult leading to complement activation is unknown and any predisposition to a prothrombotic state has the potential to increase the risk of preeclampsia. A second, larger targeted resequencing project will look at population of preeclamptic pregnancies, not just those with an autoimmune disease. Comparisons of healthy placentas with preeclamptic placentas will identify differences in complement activation between these two states. Studies in primary explants and primary human trophoblast cultures will allow the mechanisms of these changes to be studied and the effect on trophoblast cells to be followed over time. Finally, the effect of reperfusion injury in trophoblast cultures on complement activation and trophoblast state cell fate will be quantified and followed over time.